We reviewed the records of 120 women, age 35 years or younger, with the diagnosis of breast cancer at ten hospitals in the Milwaukee metropolitan population of 1 million between 1970 and 1980. We analyzed epidemiologic factors, methods of diagnosis, treatment, and mortality. While 57 per cent of the patients sought medical attention within 6 weeks of the first symptom, 34 per cent waited longer, and physicians postponed biopsy more than 2 months in another 7 per cent. Most often, the first symptom was a painless lump (61%) and the histology was ductal carcinoma (73%). Only 61 per cent of the patients had preoperative mammography, and 52 per cent of the radiographs were interpreted as benign or negative. Estrogen receptors were obtained in only 38 per cent. At the time of presentation, only 3 per cent had evidence of distant metastases. Mastectomy with or without nodal dissection and/or pectoral muscle excision was performed on 97 per cent of the patients. Twelve per cent of the patients had or developed bilateral breast cancer. Chemotherapy, irradiation, and hormone manipulation were used alone or in combination (with or without mastectomy) in 76 per cent. Although complete 10-year survival data are not yet known, 25 per cent of the 120 patients are dead of the disease and 10% are lost to follow-up and presumed dead. These data indicate that in women age 35 years or younger with breast cancer, patient and physician delay in diagnosis has been common. Estrogen receptors and mammography have been underutilized in this patient population. However, in this community, young patients fared no worse than older women.